Insulating a cathedral ceiling
I am trying to find an effective way to insulate a cathedral ceiling (with collar ties) in zone 5 south of Chicago. I have read many of the postings and have gathered much information, but am still hesitant due to the moisture drying to one side issue.
What I have is 2×6 rafters on a 4/12. I am doing a complete remodel and plan on removing the existing drywall and insulation. I want to verify the existence (or not) of ventilation chutes from eave to ridge.
I will be performing all of the work interior so as not to incur the expense of a new roof. I am going to pitch my thoughts and would welcome any feedback.
Once I have opened up the ceiling from the interior, my thoughts were to apply 1-by strips to the rafters against the roof decking to allow for some type of vent chute application up to the eave. Next, I thought I would strip out the underside of the rafter using 2×4 on edge screwed and glued to the existing 2×6. This would give me about 8 inches of useable cavity.
It is at this point I start questioning the many options available to me. Do i forego the vent chutes and simply spray closed foam on the underside of the roof sheathing, if so at what thickness? Do I utilize a firm vent chute made from some type of thin paneling/mdf/plywood and fill the remainder of the cavity with batt insulation (what type?) then fasten 2″ thick extruded poly to the underside of the rafters (drywall to follow)?
It is my understanding that I don’t want to make a sandwich using batt or blown between rigid foam board. Could someone give me some advice on what would be acceptable in regards to moisture control?
I understand I may not be able to acheive the R-value that the building code requires but I would like to acheive the best bang for my buck considering what I have to work with. Any thoughts or suggestions would be greatly appreciated.
Jon Cypert [email protected]
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